Siren



O. I. H. EKMAN March 8, 1938.

S'IREN Filed March 2, 1936 Patented Mar. 8, 1938 eAra-nr orrlce SIREN 0101 Ingemar. Harald Ekman, Stockholm, Sweden Application 'March 2,

1936,- Serial No. 66,710

In Sweden February 12, 1935 Claims.

A well-known type of sirens for signaling purposes bases its action upon the use of a fluid under pressure, usually compressed air generated by means of a rotary compressor wheel or de- 5 livered from a separate reservoir, the air being discharged from a chamber at certain determined intervals into the open air through a sound aperture or apertures from which there may lead horns for controlling the direction or directions of the sound. In sirens of this type,

the sound is produced by variations. of the pressure in said chamber obtained as a result of the alternate opening and closing of said aperture or apertures. If horns are used, they not only guide and direct the sound vibrations but act also as discharge passages for the-exhaust fluid, thereby interfering with the formation of the sound vibrations. In another well-known type of sirens, the sound producer comprises a 0: diaphragm vibrated either by means of an electromagnetic force or by the action of compressed air. In the last-mentioned case the diaphragm is situated in a sound chamber to which. leads a pipe for the compressed air in such away as to have its mouth opposite the diaphragm. The sound chamber'is provided with a horn, and the diaphragm acts as a valve for said pipe in order to periodically discharge a quantity of compressed air through the horn, thereby giving 0': rise to a natural vibration therein. In this type of sirens the force, whether it is produced by an electromagnet or by compressed air, may only act upon a restricted portion of the diaphragm near its centre, so that only diaphragms of rather v smml dimensions may be-used. In case of larger diaphragms of substantial mass, the whole diaphragm cannot take part in the vibration as a result of such a concentrated action, particu larly not at high frequencies, so that the vibra- 5 tion will be limited to the central portion of the diaphragm. As a strong sound requires a large diaphragm, the range of use of sirens of this type will be correspondingly limited. It is further to be noted that in sirens haw'ng a dia- 45. phragm operated by means of compressed air, the horn acts as an outlet for the exhaust air and will, as a result, cause such an interference with the sound vibrations as that already referred tohereinbeiore in connection with the description of the first stated type.

The object of this invention is to provide a siren by which the above stated drawbacks are overcome, and which presents, in addition, several great advantages.

The invention relates to that type of sirens in which a diaphragm is provided as a soundproducing member in a. chamber formed with a constantly open sound aperture or apertures on one side of the diaphragm. The principal characteristic feature of the invention involves that the vibrations of the diaphragm are produced by means of a fluid under pressure, that is to say, a pressure above or below atmospheric, which is intermittently admitted to the surface of the diaphragm remote from said sound aperture or apertures under the control of a valve mechanism, the operation of which is independent of the vibrations of the diaphragm.

In the accompanying drawing an embodiment of the invention is shown in axial section in the single figure In the embodiment shown the: numeral I indicates a, preferably circular, diaphragm which is inserted as an intermediate wall in a chamber formed between a bottom piece 2 and a cover 3 both of which are formed with peripheral flanges, between which the circumferential portion of the diaphragm is clamped. Said flanges are held together by screws 4% extending through suitable washers 5 of a thickness equal to that of the diaphragm, or somewhat thicker, there being left a space between the inner periphery of the annular washer and the outer periphery of the diaphragm sufficient topermit a radial expansion of the diaphragm, which is necessary, for instance, if the diaphragm, when in operation, is. heated by a hot gas used as an operating fluid. In the embodiment shown the bottom piece 2 represents at the same time an end wall of a pressure chamber 6 adapted to receive a compressed gas which may be admitted thereto by a pipe 7 or the like, leading, for instance, from a. rotary compressor located outside said chamber. Extending centrally through the chamber 6 is a rotatable shaft 8 projecting intothe space 8 between the end wall 2 and the diaphragm l and carrying in said space a disk shaped slide valve ii having twosets of apertures H, 12, concentrically surrounding the shaft 8. The apertures H are situated above a set of apertures 53 leading to the pressure chamber 6 and, similarly, the apertures l2 are situated above a set of apertures M leading to the atmosphere.

The cover 3 is. provided with a central port from whichv projects a horn i5.

The shaft 8 is adapted to be rotated at a varying number of revolutions, as for instance, by an electric motor or the like. The apertures ll, l2 of the slide valve In and the apertures l3, M of the end wall 2 are so related with'respect to each other that upon the rotation of shaft 8,1the space 9 between the diaphragm I and the slide valve III will be alternately communicatedwith the pressure chamber 6 and the atmosphere. As a result of this operation, the diaphragm will be alternately subjected to a pressure above atmospheric and to the atmospheric pressure and will, consequently, vibrate at a frequency determined by the speed of rotationof the shaft 8 and the number of apertures. When the diaphragm is pressed upwards under the action of a pressure above atmospheric, it will act as a piston in the space l6 between the diaphragm and the cover 3. The height of said space should be so determined that the principal part of the air in the chamber I6 will be discharged into the horn as a result to return to its original position by its inherent elasticity, a sound vibration will be produced. It is evident that in this operation, the horn need only act to transmit the sound vibration, but does not act as an outlet pipe for the exhaust fluid,

: because the diaphragm closes the horn with relation to the pressure chamber 6. At each vibra tion the quantity of driving fluid that may be contained in the space 9 is allowed to escape, and to each individual-tone there corresponds a definite number of such quantities. In order to avoid undue losses 'of driving fluid, it is thus advisable tomake the volume of the space 9 as small as possible by limiting the height of said space to what is strictly necessary for allowing the return vibration of the diaphragm. This is 'due to the'fact that the diaphragm also performs a fully developed negative vibration, below its central position.

The apertures formed in the slide valve and the rigid end wall 2, by which the frequency is determined, act also to determine to a certain ex tent the curve representi'ngth'e vibrations of the diaphragm. It is thus possible,'by suitably shaping these apertures, to obtain an adequate shape of this curve, allowing the apertures to regulate the admission and discharge of the driving fluid and thus also the variations of pressure upon the diaphragm in agreement with each angular variation during the rotation of the slide valve in a predetermined manner. If desired, provisions 'may be made toallow the driving fluid to expand in a certain degreein the space 9 below the diaphragm before discharged to the atmosphere.

It has been stated hereinbefore that the use of a fluid under pressure for the operation of the diaphragm in the manner described involves that the power will act simultaneously upon the whole diaphragm, as distinguished, for instance, from p the action of an electromagnetic or mechanical through the slide valve apertures of the siren in-,v

creases with increasing pressure, it is easy'to -raise the frequency very high and to vary the force acting upon the diaphragm.

Variations relating to the construction may be made in many ways without departing from the principle of the invention.

What I claim is:

l; A siren, comprising means'formin'g. a chamber, a diaphragm inserted as a sound producing member in said chamber so as to divide it into two spaces, said chamber having a constantly open sound emission port opening to one of said spaces, said chamber also having'separate admission and discharge apertures opening to the other of said spaces fora driving fluid, a rotary slide valve having apertures to control both said admission and said discharge apertures so as to alternately admit and discharge driving fluid to and from said other space.

2. A siren, comprising means forming a sound chamber having two oppositely disposed walls, one of said walls having a constantly open sound port, a diaphragm inserted in said chamber so as to divide it into two separate spaces, each facing a separate one of said walls, means forming a. driving fluid chamber situated outside the other one of said walls, said other wall having a set of apertures connecting the driving fluid chamber with the space facing said other wall, said other wall having another set of apertures leading from the space between the diaphragm and the said,

other wall to the atmosphere, and a rotary slide valve having apertures therein inserted in said last-mentioned space to control said two sets of apertures in alternation. i

3. A siren, comprising two end walls and a. peripheral wall forming a sound chamber, one of said end walls having a constantly open sound port, a diaphragm mounted in said chamber clamped loosely at its periphery in said peripheral wall to allow of expansion thereof, said diaphragm dividing the sound chamber into two separate spaces, each facing a separate one of the end walls, means forming a driving fluid chamber.

outside the other end wall, said other end wall having a set of apertures, communicating the driving fluid chamber with the space adjacent said other wall, said other wall being provided with another set of apertures leading from the space between the diaphragm and the said other wall to the atmosphere, and a rotary slide valve having apertures therein inserted in said lastmentioned space to control said two sets of apertures in alternation.

4. A siren having, in combination, means form,-

ing a sound chamber said means including two end walls and a peripheral wall, one of said end walls having a sound emission port and the other end wall having inlet and? outlet apertures for a driving fluid, a diaphragm inserted in said 'pe-- ripheral wall so as to divide the'sound chamber into two separate spaces each facing, an individual one of said end walls, both of said spaceshaving a height perpendicular to the diaphragm which is substantially only as great as is necessary to permit the vibrations of the diaphragm' and a rotary'valve having apertures therein for controlling said inlet and outlet aperturesmounted adjacent said other end wall.

5. A siren as claimed in claim 1, in which the discharge aperture of the other-chamber is situated near its periphery in order to allow the fluid to be discharged, in part, by centrifugal force.

OLOF ,INGEMAR HARVAIJD the action of i 

